A Audi Q7 4.2L car with a mileage of about 146 thousand KM. User reflection: the vehicle is unbrake in the vehicle. Fault diagnosis: (1) the car replaced the front and back brake disc and the front and back brake disc, two months after the customer reflected the vehicle driving about ten thousand meters after stopping to take things, after taking things out of the starting driving brake without braking, brake pedal in the end, vehicles continue to move forward. Then the flameout hand brake vehicle stopped. Then call the rescue and drag the car to my station. (2) PQA teachers and foreign experts go to the scene to check the car inspection process: first check the brake oil and check the water content with special tools. After trial run, it was found that the vehicle had two front wheels to hold the brake. There were two possible analyses: the sub pump and the components after the pump. When we dismantle the two pre pump, it is found that some of the piston in the sub pump have no back position in the free state, and the final analysis is that the back position of the left and right brake pumps is bad and the brake disc is worn off and the brake disc is discoloring. The expert recommends that a pair of front brake disc and the left and right front wheel brake assembly be replaced and the quick return analysis is used. Troubleshooting: replace a front brake pad and front and rear brake caliper assembly.